This study is designed to isolate, identify and characterize the pharmacological actions of the antifibrillatory substance "pteryxin" in the roots of the plant Pteryxia terebinthina. Standard solvent fractionation procedures will be employed together with chromatographic procedures to separate the active principles. Briefly, the plant material will be extracted with Skellysolve B and other solvents and crystallized. The crystalline material will then be subjected to a series of pharmacological testing involving both in vivo experiments to determine the antifibrillatory actions of this substance. Standard antiarrhythmic drugs such as quinidine, procainamide, lidocaine and the beta adrenergic receptor blocking agent will be used as a basis for comparison of the antifibrillatory potency of the active substance in pteryxin.